.b{
    transition: height 0.2s ;
    position: absolute;
    top:0;
    z-index: -1;
    width: 100vw;
    display: flex;
    justify-content: center;
    align-items: center;
    color:white;
    background-size: 200%;
    animation: alphaGradient 3s alternate infinite;
    background-image: linear-gradient(45deg,#ff5252 30%,#b33939 60%,#ff793f 100%);
}

@keyframes alphaGradient {
    0%{
        background-position: 0 50%;
    }
    50%{
        background-position: 100% 50% ;
    }
    100%{
        background-position: 50% 0;
    }
}